With an X-Y address type solid-state image pickup device such as a CMOS image pickup device or the like, an output signal which is substantially linearly proportional to the amount of charges accumulated in each unit pixel through photoelectric conversion is obtained, and the dynamic range of the image pickup device is determined by the amount of charges which can be accumulated in each unit pixel.
FIG. 13 is an input/output characteristic diagram showing the relationship between the amount of light incident to an image pickup device and the output signal amount thereof. Apparent from the input/output characteristic diagram, the dynamic range of the image pickup device is determined by the saturated signal amount of each pixel and the noise level.
As described above, the charge amount which can be accumulated in the unit pixel is restricted due to the size of the pixel. Therefore, if the diaphragm of a camera lens is matched with a subject having low brightness in a camera system using this type of X-Y address type solid-state image pickup device as an image pickup device, the signal of a subject having high brightness is saturated. On the other hand, if the diaphragm of the camera lens is matched with a subject having high brightness, the signal of a subject having low brightness is embedded in noises, so that a broad dynamic range required for image recognition, etc. cannot be obtained.
Therefore, there has been proposed an X-Y address type solid-state image pickup device which can implement a broad dynamic range image pickup operation by outputting both of a long-time accumulated signal and a short-time accumulated signal during one field or one frame and obtaining an image pickup signal having contrast to an incident light amount in a very broad range on the basis of the long-time and short-time accumulated signals. Here, the long-time accumulated signal is a signal based on signal charges which are accumulated for a long time, and the short-time accumulated signal is a signal based on signal charges which are accumulated for a short time.
In the conventional X-Y address type solid-state image pickup device, the long-time accumulated signal of one line is output and then the short-time accumulate signal of one line is output. Therefore, a vertical read-out scan pulse rises up during a horizontal picture period or a horizontal scan circuit carries out a scanning operation twice during one horizontal scan period, which leaks into a camera signal processing circuit and appears as a vertically-striped system noise in the vicinity of the center portion of the screen.
Further, the long-time accumulated signal and the short-time accumulated signal are output from a single output terminal through a common signal line during the same horizontal scanning period, and thus the output signal frequency is increased substantially twice for an image pickup device which does not carry out the broad dynamic range image pickup operation. Therefore, the power consumption is increased and the SN ratio is deteriorated.